Ocean heat content increases update

There is a new paper in Nature this week on recent trends in ocean heat content from a large group of oceanographers led by John Lyman at PMEL. Their target is the uncertainty surrounding the various efforts to create a homogenised ocean heat content data set that deals appropriately with the various instrument changes and coverage biases that have plagued previous attempts.

We have discussed this issue a number of times because of its importance in diagnosing the long term radiative imbalance of the atmosphere. Basically, if there has been more energy coming in at the top than is leaving, then it has to have been going somewhere – and that somewhere is mainly the ocean. (Other reservoirs for this energy, like the land surface or melting ice, are much smaller, and can be neglected for the most part).

The main problem has been that over time the network of XBT probes and CTD casts has been replaced by the Argo float network which has a much greater coverage and more homogeneous instrumentation. However, connecting up the old and new networks, and dealing with specific biases in the XBT probes is difficult. An XBT (eXpendable Bathy-Thermograph) is a probe that is thrown off the ship and whose temperature readings as a function of time are transferred to a profile in depth from knowledge of how fast the probe falls. Unfortunately, this function is a complicated one that depends on the temperature of the water, the depth, the manufacturer of the probe etc. Various groups – working with the same basic data – have shown that there were biases in the XBT associated with incorrect calibrations and have attempted to make better corrections.

The latest paper is a consensus effort from many of the people involved in the previous work and shows how robust the recent decades warming of the ocean has been. Indeed, the ‘best estimate’ for the changes in the top 700m seems to be a greater warming than seen in the NODC data and more than even the models were suggesting:

Update (May 2012): The scaling of the model output on the original graph was incorrect, and the graph has been replaced with a corrected version. The original can still be found here.

One thing that is interesting to note is that the interannual variability – particularly in the transition period between the two observing systems (1995-2005 say) is very dependent on exactly how you do the corrections, while the longer term trend is robust. This ties in directly with comments by Kevin Trenberth in this recent paper and in an accompanying commentary to the Lyman paper that while the energy budget changes over the long term are explainable, the changes over short time frames are still very difficult to quantify.

As usual, this is unlikely to be the very last word on the subject, but this is more evidence that the planet is basically behaving as the scientists think it is. And that isn’t necessarily good news.

169 Responses to “Ocean heat content increases update”

re:130. Whoops, my bad. I misread the units on the graph. Doesn’t make any difference to the discussion though. Whatever the units, an error of 2.5 out of ~8 is a very large degree of error.

The obvious offset in the data during the transition from XBT to Argo is a much more interesting and useful item to examine. Once you’ve established what the data really is then you can go on to deal with the actual heat content changes are.

Another point on this, the heat content is the change in temperature at particular points in the ocean. The publicly available abstract makes the point that the dominant effect was the choice of method for making adjustments(correcting biases) to the data. However, the major conclusions shown are about the change in heat content(temperature) estimates. The meat of the matter is why the different adjustment procedures don’t agree and if there is any way to get accurate enough temperature estimates to make useful estimates of the accumulated energy.

The phrase “Accounting for multiple sources of uncertainty, a composite of several OHCA curves using different XBT bias corrections” raises a red flag to me. Sounds very much like picking dates when calculating temperature trends.

[Response: You have misunderstood more than the units. The whole point of the paper was to investigate whether the different correction techniques made a difference to the underlying trend – and the answer is that they don’t very much. That is, warming of the oceans is robust to the differences in approach. This does not mean we know what the exact right approach to those corrections are – but it does mean that you can be more aware of what the impact of those uncertainties are. They matter for the year-to-year variability, but not the trend. This is the complete opposite of picking one set of corrections that you ‘like’ and just going with that. – gavin]

I think the question is one of “was there a time without a permenant ice pack” rather than “ice free.”

The answer is a tough one. We know that Antartica froze in the winter even in the late Jurrasic, forcing hibernation of the dinosaurs (if we’re to believe the exellent Walking With Dinosaurs series. ;) ).

I was thnking in the era more of when ice ages have occured and when there has been permenent ice at the poles. The planet developed permanent ice at the poles when GHG/C02 levels dropped low enough due to weathering when India met Asia or so the present level of knowledge appears to be telling us.

We are not going to avoif 450 ppmv of Co2 let alone the other GHG’s so we had better find out. Some stuff I have read over the years seemed to point to a lot less ice when CO2 levels were anything from 450 to 700.

Well, it isn’t ocean *heat* content, but relevant to climate science in various ways is this story, about quantifying the methane released by the Gulf blowout (roughly estimated at about 7.5 kilotons so far.)

assuming it is correct as asserted by Alastiar McDonald that the Arctic has lost 14,000 cubic kilometres of ice since 1980… (any reference anyone?)then the latent heat abosrbed from the ocean to melt it is is approximately 0.5 8 10^22 Joules so the heat content of the ocean would need to be adjusted upward to refect
t this gain in heat ( not temperature ) .. think its called enthalpy!

CFU, I was asking about colin Aldridge’s post which didn’t refer to radiation.

Radiation absorbed in ice would do the same thing as you say. I’m not sure how realistic that is; Doesn’t the preponderance of polar sea ice melting come from ocean heat, not radiation? (Hmmm. Or rather is it the ocean the that causes most of the melting of only that ice that exceeds the norm???)

Did you know that the sun radiates the earth, Rod?
You see, without any new input of energy, what happens is that the water and ice reach an equilibrium. The water gets cooled by the near ice and the ice warmed, but they will reach 0C where H2O can be either water or ice.

Some of the water will freeze because it gives it’s energy to the ice and some of the ice will melt, taking heat from the water.

Melting the ice requires that more energy goes in.

Either by replacing the cold water with warmer water (ocean currents) or by the sun warming the ice and melting it.

If the sun is doing it, it has to do it with radiation. There’s no conduction or convection to do it across 93 million miles of vacuum.

Gavin, Interesting post as usual. One explanation by oceanographers, such as Mojib Latif, to partly explain the increase in temperatures in the 90s is that of a net transfer of heat from the oceans to the atmosphere. From the Argo temperature probes, calculating vertical temperature gradients throughout the 700 m depth should be able to tell whether or not the heating is coming mostly from the surface (i.e. due to SW solar and LW radiation absorption in the top layers of the ocean) or from the ocean depth. Has the net heat transfer from the surface been calculated from the temperature profiles ? Why can’t the spatial distribution of the Argo probe temperatures inform us on where the heat is coming from or going to?

[Response: I think there is some more information to be derived from this data, but the regional information has bigger uncertainties, and more internal variability. -gavin]

Thanks for the reply Gavin. Although satellites can used for example to obtain spatial distribution of temperature, clouds, water vapour, aerosols in the atmosphere it appears much more difficult to measure the physical characteristics of the oceans for example the distribution of the optical depth of the particles in the oceans. The temperature distribution in the oceans has to be interpolated from the localized temperature readings of the Argo probes. In contrast, the surface temperatures (on land) can be measured more easily and the atmospheric temperatures can be measured also by satellites. It appears that our understanding of the dynamics of the oceans is much less than for the atmosphere. How do we know that the radiation absorption and emissivity of the oceans is not changing over multi-decadal scales which would affect the heat content of the oceans?

Actually, gavin is right about the column integrated ocean heat uptake, but if you’re interested in SST’s then yes….hurricanes do somewhat act as a vacuum cleaner. This video shows the time-evolution of the 2008 hurricane season with SST’s, and if are patient enough to watch you will see that cyclones passing by leave a trail of relatively cool surface temperatures. The first good example is at the right of the screen about 1:00 in. There’s a pronounced effect from one about 2:35 in to the video.

Interestingly, there’s a recent paper out which suggests that ocean heat uptake due to tropical cyclone upper ocean mixing has been significantly overestimated in the past, so it’ll be interesting to see how this develops in the community.

For a clarification of my previous comment, it does appear as a “vacuum cleaner” effect though the cooling mechanism is moreso associated with entrainment of colder water induced by vertical mixing rather than by air/sea heat loss

This is a really great website! lots of excellent and well sourced information!
The temperature of the oceans is an interesting one, and one that we don’t seem to know that much about unfortunately. We have lots of data on the surface temperatures and now even the top 700m of water or so, but there is so much energy storage in the deeper oceans that we unfortunately don’t know all that much about. I guess tho since the deep oceans take so long to turn over most of the warming of the last century would show up in the top 700m anyway.

I was reading about Roy Spencer, he believes that the climate sensitivity is not as large as we had originally thought, he says to account for recent warming we need to look at the oceans and the Pacific Decadal Oscillations. I’m not an oceanographer but the figure on his site ( http://www.drroyspencer.com/global-warming-background-articles/the-pacific-decadal-oscillation/ ) that shows El Nino and La Nina over the last 100 years appears to show a correlation between global temperature and a 30 year cycle of El Nino and La Nina. The figure shows a high around 1935, a low around 1960 and the latest high around the year 2000. Just wondering what more informed minds thought of him or his science? Or any comments about any of his interpretation of data?